Navigational instrument



Feb. 15, 1938. c. w. HARRIS 2,108,260

NAVIGATIONAL INSTRUMENT Filed June 14, 1955 2 Sheets-Sheet 1 awe/rmFig.5 Charle W. Harrifi Feb. 15, 1938. c. w. HARRIS v 2,108,26

NAVIGATIONAL INSTRUMENT Filed June 14, 1955 2 Sheets-Sheet 2JJIHIIIHIIIHIIII .2 Fig.6.

- I2 I i 2 I6 H l4 2 CharlesVHarris Patented F b. is, 1938 UNITED STATESPATENT ori-lea My invention relates to an instrument for use in solvingproblems arising in navigation.

One of the most tedious and exacting parts of the routine of a navigatorwhich must be gone through several times daily, and one which is liableto error, either from mathematics or from incorrect reading of tables,is the determination of a ships position. Various methods have beenemployed for such determinations. To carry out some of them it was atone time considered necessary to have available a large number of tablesreading in seconds, or, if the number of tables was to be made less (forexample, down to tenths of minutes), interpolation must be resorted to,and still a large number of tables must be available. To somewhatsimplify these operations, newer methods have been adopted which requirethe assumption that a vessel is at a location where it is known shecannot reasonably be, and then by a series of calculations (based onobservation) to obtain her line of-position, but since indirectcomputation and unnecessary assumption is required in carrying out thismethod, the probability of error is greatly increased.

In all such previous methods resort must be had to a variety of tables,thus introducing the possibility of error through the incorrect readingof the tables, as well as in the attending calculation. It is thereforea primary object of this invention to eliminate any reference tocomputational tables, and similarly to confine the calcul'ationto thesimple operation relating to time, to the end that by the most directmethod the azimuth and computed altitude of the observed celestial bodymay be obtained, from which a line of position may be plotted so thatwith another related observation there can be obtained, in a minimum oftime and with a minimum chance of error, the exact location or fix ofthe ship's position.

More specifically it is an object to provide a precision device orinstrument of a convenient size, which can be made as accurate as thesextant and reading in the same familiar and uniformly graduated unitsof arc, which will serve as a calculator, taking into consideration theD. R. latitude, the hour-angle at the instant of observation, and thedeclination of the observed body at the instant of observation, thus tocalculate automatically and give immediately to the navigator theazimuth of the observed body and the altitude thereof for comparisonwith the ob served altitude obtained by the sextant observation. Thusthe navigator requires only his sextant and his Nautical Almanac andchronometer, and need not refer to such tables, for example, as arecontained in Dreisonstok or in Hydrographic Offlce Publication No. 211.

Since an instrument of this sort must be very accurate, and may berendered inaccurate from 5 loose bearings, wear of parts, slightinaccuracies of scale graduation or in the manufacture of parts, or likecauses, arising during manufacture or during use, and such extremeaccuracy would be required as to be impractical commercially to avoidcertain of these inaccuracies, and even so those arising from use wouldbe unavoidable, it is a further object to provide means whereby toadjust the instrument, according to a correction table, to compensatefor such inaccuracies, thereby enabling the commercial production of theinstrument at a reasonable cost.

Other objects, more especially such as relate to details or toconstruction, will become apparent as this specification progresses. 20

My invention comprises the novel instrument, and the novel parts andrelative arrangement of the same, as shown in the accompanying drawingsin a preferred form, which form will be described, and the principles ofmy invention made clear, in this specification, and the scope thereofaccurately defined by the appended claims.

Figure 1 is a perspective view of the instrument set in positionaccording to certain observations to obtain an azimuth and altitudereading, the altitude indicator beingshown as provided with means toadjust for localized instrumental errors.

Figure 2 is a plan view of the instrument, certain parts having beenaltered in position from the position of Figure 1 for betterillustration, and the altitude indicator being of a somewhat modifiedconstruction.

Figure 3 is a cross section on the line 3-3 of Figure 2, parts beingagain changed in position, and Figure 4 is a similar section on linel--4 of Figure 2, with parts substantially in the position of Figure 3.

Figure 5 is a detailelevation, partly broken away, and Figure 6 is asection on line 6--6 of Figure 5, illustrating the means to adjust forlocalized instrumental errors.

Essentially my device comprises five different indicators-a latitudeindicator, an hour-angle indicator, a declination indicator, an altitudeindicator, and an azimuth indicator. In the sense which I here use theterm indicator it is to be understood as meaning a circular scale and acooperating index, and it is largely immaterial whether the index rotaterelatively tov the scale, or the scale relatively to the index; hencewhile I shall now proceed to describe the instrument in detail, it mustbe borne in mind that changes such as those suggested and others may bemade as the skill of the navigator or designer of such instruments woulddictate.

The latitude indicator, in the present instrument, consists of acircular base 9 bearing the scale L, with which cooperates a table 9!!bearing the index 1, the table being rotatable about an axis a (seeFigure 1). Any suitable pivot arrangement which will be sumcientlyaccurate may be employed. Thus a headed pin 9I projects upwardly fromthe base 9 and is received in a boss 92 formed at the center of thetable 90. Balls 93 or similar antiiriction means may be employed topermit the table to rotate readily. The table is held in place by thecollar 94, and rotation may be given to it in any suitable manner, asfor example by a pinion (not shown) engageable with the circular rack 95and rotatable by means of the thumb screw 95. The scale L preferablyextends 90 or more in each direction from a zero point, and the index I(as well as other indices hereafter described) is preferably a Vernierindex.

Disposed equatorially with respect to the latitud'e scale L is anhour-angle indicator, consisting of the circular are 8, the feet 88 ofwhich are received immovably between ears 98 of the base 9, this are 8,which lies in a plane normal to the polar axis of the latitude scale L,bearing an hour-angle scale H. An index h moves along and cooperateswith this circular scale. It may be formed upon a slide 89, and itsmovement may be controlled by means of a worm pinion (not shown) mountedin the slide 80, rotatable by means of the thumb screw 85 and engageablewith teeth 85 upon the periphery of the are 8.

The slide 80, carrying the hour-angle index h, is fixed to the centralpart of an arc I pivoted upon an axis 5 which is parallel to the polaraxis of the latitude scale L. The are I, however, is always in a planenormal to the are 8 bearing the hour-angle scale H. It may be supportedfor tilting movement upon trunnions II supported in posts 91 fixed toand projecting above the base 9. By such means the hour-angle index isrotatable about the axis 5, which is perpendicular to the axis a (seeFigure 1). The are 1 carries an angular declination scale D, and a slideI carrying an index at cooperates with the scale D to indicatedeclination. The movement of the slide TI) may be controlled as theother indicators were controlled, for example, a thumb screw I8 beingprovided for the purpose, and the are 1 bearing teeth I to accomplishits control.

It may be stated here that of the table 9, the slide 80 and the slideHi, all may be controlled in corresponding fashion, and each of them maybe provided with clamp means so that they may be clamped at any givensetting, but as such means are well known in the instrument art, and ofthemselves form no particular part of my invention, they have beenomitted for clearer illustration.

It may now be pointed out that the index I0 is rotatable about an axis7, which is perpendicular to the axis 3, but which will only beperpendicular to the axis a in the special case when the hour-angle is90. However, the three axes, a, ,8, and all intersect at a common point.

Upon posts 99, rising from the table 90, is ti t-ably mounted asemi-circular plate or arc I. This bears a scale A, which is thealtitude scale, and with it cooperates an index a carried by an arm l9pivoted to the plate I to swing about an axis 6 perpendicular to theplane of plate P. A pivot post II passes through the plate I and armIII, and has suflicient bearing that the arm with its index a movesaccurately over the scale A.

At its peripheral end the arm I0 may be pr vided with a windowed headI2, which carries the index a, which head is in turn pivotally connectedto the slide III by a pivot pin II, so that the entire plate I inefl'ect rotates about an axis e which coincides with the axis of thepivot pin I1, and which in turn passes through the point common to theaxes a, p, 'y, and also a. The tilting'of the plate I on the post 99 isabout an axis x, which is parallel to the plane of the latitudeindicator, and this axis K again intersects all the other axes at thecommon point, which may be likened to a geocentric'point.

Arranged in a plane normal to the axis K, and therefore normal to theplate I which is in a radial plane with respect to the axis x, is acircular plate 2. This plate 2 is secured to the plate I to swing withthe latter about the axis x, and the plate 2 bears an azimuth scale Z.Cooperating with this scale Z is an index z which may, for example, befixed upon one of the posts 99.

Instead of scribing the index a d'rectly on the head I2, it ispreferable that it be scribed on a slide I3, adjustable transversely ofthe head I2 by means such as the pinion I5, carried by the arm I0,meshing with the rack I6 on slide I3, and'rotatable by the adjustingscrew I4. An instrument such as this, no matter how carefully made, issubject to localized instrumental errors, or may become erroneousthrough distortion or abuse of parts. Such errors may be cumulative atthe altitude index, hence compensatory-adjustmcnt at this point isparticularly desirable; however, similar adjustment may be made at eachindex, if desired.

It is possible, by setting the several indices at definite points, andby reference to tables and calculations as now commonly employed, todetermine if it reads correctly. For example, at a given latitude, agiven hour-angle, and a given declination, the altitude reading shouldbe always the same, and should correspond exactly to the computedaltitude as determined from tables and calculations. If the instrumentalreading does not exactly correspond (though it can be made accuratewithin the usually required range of accuracy for ordinary navigation),the index a can be adjusted to correspond exactly, and its variation forthis latitude, hour-angle, and declination noted. By similarly checkingthe instrument for every degree, or for every five or ten degrees, atable of correct readings for every range of settings can be obtained,and adjustment may be made for such localized instrumental errors whenextremely accurate navigation requires it.

For the purpose of illustrating the use of this instrument one mayassume a ship to be in the general position of the northern extremity ofVancouver Island in the North Pacific, say 4926.4' N. Lat. and 13637.2'W. Long., as determined by the customary D. R. method. By observation inthe early morning the navigator finds the sextant altitude of the sun,and records this altitude together with the exact time by chronometer.By means of the Nautical Almanac, using the recorded time and the D. R.longitude, the exact hour-angle of the sun is found. This may includefractional minutes of arc, as for example 6818.7'. 'lhe declination ofthe sun at .the instant of observation is also available in the NauticalAlmanac. and on this particular instant and date in the autumn was1059.1' S, All of this information is obtained from the sextant andchronometer reading, and from the Nautical Almanac. It is now desired tomake correction to the D. R. position'by applying the usual "computedaltitude method. The present instrument. now comes into use, and is setaccurately in a position roughly shown in Figure l, and gives thedesired .altitude and azimuth upon setting the latitude of the D. R.position and the hour-angle and declination and azimuth are givenwithout reference to logarithms or other computing ta-' bles, andwithout the aid of any assumed position other than the D. R. positionfirst recorded.

Procedure is as iollows: First, on the latitude scale L, set of! the D.R. latitude, in this .case 4926.4 N. Second, on scale H, the hour-anglescale, set of! the hour-angle, 6818.'l'. Third, on scale D, thedeclination circle, set 01! the declination, 1059.1' S. The desiredcomputed altitude" the" diflerence in minutes between the observedsextant altitude and the instrumentally determined "computed altitude"..The direction in which the correction is to be made is shown by theinstrumentally determined azimuth, the corrected position being towardthe sun, ii the sextant altitude is larger than now be drawn through thecorrected point and perpendlclfllto the azimuth. 1i fix may thus bedetermined by the intersection of two such lines of tion madesimultaneously by observation on two celestial objects, or by two solarobservations taken with the sun at diiierent azimuths, and with properconsideration of intervening distance run by the ship. In other words,the "computed altitude and the azimuth may be obtained by direct readingirom the instrument without reference to tables, and may be 50 usedexactly as is used the"computed altitude obtained from tables, and theazimuth, but the navigator is not required to go through a lengthy andinvolved computation, with the possibility of mathematical error, andwith the possibility as oi incorrectly-reading tables.

Itwili be observedthatwhenanythreeoi the quantities are known. and thecorresponding scales areset, the other two quantities become known.Hence while ior most purposes the instrument willbe operated in themanner described,itrnaybeusedin otherwayathatisto say, to obtain alatitude reading, knowing the a hour angle, declination and altitude orazimuth.

In aerial navigation the methods heretoiore used, requiring extensiveence to tables. are unsatisfactory because oi the speedoitheaircrait.placing itmanymilesirom acalculatedsumneriinebeiorethatlineisdetermined,andbecause of the limitations oi space andweightiorcarryingtables,andiurtherbecauseitisusuallyimpracticalforthepllot'todo the navigating,necessitating an extraman, with his added ws is pm'oll ior navigating.This oi the sun is then read from the scale A, the

the "computed altitude", and conversely. The line of position may ablewith and secured'to calculation and reier- 'orscales and indexesinstrument eliminates the necessity for carrying or reierring to tables,and makes it possible ior the pilot, with but little distraction fromhis other index swingable along the declination scale, a

pivoted altitude scale, an altitude index swingable along said altitudescale and pivotally connected to said declination index to moveconjointly'therewith but swingable relatively thereto, a latitudeindicator disposed at all times in a plane normal to the plane of saidhour-angle indicator, and including an index rotatable about an axis inthe plane oi the hour-angle scale and normal to the pivot axis of thealtitude scale, a pivoted azimuth indicator disposed .at all times in aplane normal to the plane of said altitude indicator, the axes oirotation of said hourangle index, declination index, altitude index,azimuth indicator, and latitude index being so interrelated as tointersect in a common point, and means interconnecting said latitude andazimuth indicators with said hour-angle, declination and altitude scalesand indexes to eflect movement oi any two of such indicators or scalesand indexes, to designate resultant characteristics, in response tomovement 01 the other three indicators or scales and indexes intopositions corresponding respectively to known or given characteristics.

2. A navigational instrument comprising a base member, a pivoted memberdisposed parallel to said base member, one oi said members bearing alatitude scale and the other a latitude index to constitute a rotatablelatitude indicator, an arcu- 1 ate hour-angle scale fixed to said basemember in a position extending'thereabove in a plane normal to said basemember, a declination scale pivotally supported from said base memberand disposed at all times beneath and in a plane normal to saidhour-angle scale, an hour-angle index fixed upon said declination scalein a position extending upwardly therefrom to move over said hour-anglescale as the index swings with the declination scale. an altitude scalepivotally supported from said pivoted member and disposed below saiddeclination'scale, an altitude index arm pivoted on said altitude scale,a declination index swingable along said declination scale and pivotallysecured to said' altitude index arm to move coniointly therewith butswingable with respect thereto, and an azimuth indicator swingsaidaltitude scale'in a plane always normal thereto, the axes of rota- 'tionoi said latitude indicator, hour-angle index,

